Spring 2017

Research Update: Meta-analysis shows PrEP is effective in women with high adherence

What do we know about PrEP effectiveness in women?

Evidence suggests that oral pre-exposure prophylaxis (PrEP) is as effective for women as it is for men when used consistently and correctly, although adherence may be more important for women. While PrEP has demonstrated high levels of effectiveness in research conducted among gay men and other men who have sex with men (MSM),1 research in women has shown mixed results.2,3,4,5,6 Of the five randomized controlled trials (RCTs) that included women,2,3,4,5,6 two trials (in women alone) found that a daily oral PrEP regimen was not effective at reducing the risk of HIV transmission.2,3 Very low levels of adherence to daily PrEP (less than 30%) among women in these two studies is likely responsible for the lack of effectiveness observed. Other trials5,6 have shown that, with good adherence, PrEP is very effective at reducing the risk for HIV transmission in women.

Biological differences in the way that PrEP accumulates in the body may be partly responsible for the mixed results observed in women. Pharmacokinetic evidence shows that PrEP concentrations are lower in the vagina (compared to the rectum), meaning that high adherence to daily PrEP may be especially important for women exposed to HIV through vaginal sex.7,8

Meta-analysis looks at adherence and effectiveness in women

A new meta-analysis used data from the five RCTs conducted in women to estimate the effectiveness of daily oral PrEP in women with varying levels of adherence.9 These five studies were conducted in different populations of women:

Two studies enrolled individual African women at risk of HIV through sexual exposure2,3

Two studies enrolled African women and men at risk of HIV through sexual exposure (one enrolled individuals4 and the other enrolled heterosexual serodiscordant couples)5

One study enrolled individual women and men in Thailand who inject drugs and may be at risk of HIV through sex and/or sharing needles and other injection drug-use equipment6

While PrEP is currently available as a two-drug combination (TDF and FTC) under the brand name Truvada, some participants in these studies were taking the two-drug combination and some were taking a version of PrEP containing TDF alone. In these studies, the two-drug formulation of PrEP was more effective at preventing HIV transmission when compared to TDF alone;2,5 however, participants taking both versions of PrEP were included in this analysis.

Results

This study found a strong relationship between adherence to PrEP and effectiveness. A combined analysis of the results from all five studies estimated that PrEP reduced the risk of HIV infection by:

36% among all women who participated in these studies (note that this estimate reflects a wide range of adherence levels, including many women who were not adherent at all to PrEP), and

61% among women with 75% adherence to PrEP, based on PrEP levels detected in the blood.

What does this mean for Canadian service providers?

Evidence from multiple studies in different populations tells us that PrEP effectiveness increases with higher adherence to the medication as prescribed.1,2,3,4,5,6 This meta-analysis demonstrates that 75% adherence to daily PrEP may not be enough for women to obtain the high levels of effectiveness seen in MSM with moderate-to-high adherence. For example, the iPrEX trial found that MSM who had any PrEP detected in their blood (and were not necessarily highly adherent) had a 92% reduced risk of HIV transmission compared to those without PrEP in the blood.1

This meta-analysis does not provide an estimate for women with optimal adherence to daily PrEP. An adherence-based analysis from the Partners PrEP study of heterosexual serodiscordant couples found that women who were highly adherent to PrEP had high levels of protection.10 The Partners PrEP analysis found a 92% reduced risk of HIV infection among women who had PrEP (TDF/FTC) blood-levels consistent with daily dosing.10

Overall low adherence among women in two trials likely contributed to the relatively low effectiveness estimate in this meta-analysis. Research has identified that women in these studies were not taking the PrEP medications given to them for many reasons, such as stigma, mistrust of the research and fear of side-effects.11 Although these may not apply for women in the current Canadian context, it will be necessary for service providers to stress the importance of adherence for women taking PrEP. It is important for service providers to discuss and assess adherence in all clients taking PrEP and provide adherence counselling if necessary.

About the author(s)

Camille Arkell is CATIE’s Knowledge Specialist, Biomedical Science of Prevention. She has a Master’s of Public Health degree in Health Promotion from the University of Toronto, and has been working in HIV education and research since 2010.

Please note that some content on this website contains language, information and images related to sexuality and drug use, and may not be intended for people of all ages. CATIE ensures that these resources, developed to help prevent the transmission of HIV, hepatitis C and other infections, are written and reviewed by health experts for content accuracy.